[Roostie]

Alignment, and the best non-run-flat summer performance tires, once your current tires wear out. Tire quality is considerably more important than trying to squeeze the largest possible tire that will fit on the rim.

I don't know if you have experience taking driving schools, doing autocross or previous track days.
It is usually good advice to start working on your own experience and training before modifying the car. A professional driver in a base SS could run circles around most of us 1LE forum jockeys ...
When you improve your skills, then you can get a lot more out of any mod. And the seat time is so fun - that's the juice, to me. The big-name driving schools like Bondurant are quite expensive but there are a lot of pretty good, cheaper options from organizations like BMWCCA, SCCA, etc. See what's available in the Bay Area, I am sure you have many options.